1. Technical Field
The present invention relates generally to communications and, more specifically, to a system and method for wireless communications among computers and other pervasive processing devices.
2. Description of the Related Art
As processing devices become less expensive and more compact, the all-purpose desktop computer is giving way to a new generation of embedded or “smart” devices such as video phones, interactive kiosks, and embedded household devices such as intelligent refrigerators, smart TVs, and intelligent dishwashers. Embedded devices are devices embedded with computing capability, making these devices “intelligent”.
As embedded devices become more widely used, they need to be able to communicate and exchange information with each other. For example, a video phone must be able to transmit and receive information with other video phones for effective communication.
Communication between computers is typically trough a communication network, in which computers are connected to each other or to peripherals by hard wire. This technique has a number of disadvantages. For example, cable connection interfaces such as parallel printer ports, are limited in the distance they can reliably transfer data. In addition, coaxial cables, which are used for longer distance hard wire communications, require a relatively expensive terminal interface and therefore are not widely used for connecting peripheral devices to computers. Moreover, when computers are hard-wired, any movement or change in the physical locations of the computers requires rewiring and reinstallation.
The prior art teaches communication between embedded devices similar to the communication between computers, as well as existing wireless communication techniques. For example, U.S. Pat. No. 5,613,070 discloses, a system for providing improved communication to data and computer communications network using parallel and serial communication buses and master and local routers. Communication through said network includes use of a master system board with a plurality of subsystem boards.
U.S. Pat. No. 5,369,755 discloses a computer communication bus system using multiple content induced transaction overlap (CITO) communication channels having a plurality of data transmission lines and a plurality of transmission nodes connected to the communication bus. Each transmission node has a data source providing multi-bit data to be transmitted on the communication bus, a plurality of data transformers for encoding or transforming the multi-bit data into different multi-bit encoded data formats, and a plurality of CITO transmitters for transmitting the a content induced transaction overlap (CITO) protocol. Using the CITO protocol, the CITO transmitters transmit the same data on each of the transmission lines in a different order.
Another form of communication between embedded devices is wireless communication. Existing wireless technology includes microwave systems, infrared laser systems, or spread spectrum. However, all these approaches have various disadvantages, including health concerns due to radiation emission and interference of signals.
Microwave is the oldest technology for wireless communications. For decades, most major telecommunications companies have used microwave systems within their networks for transmission of telephone communications, data and video. However, this form of wireless communication has significant disadvantages. For example, microwave signals travel in straight lines and do not readily diffract around barriers such as large man-made structures, hills and mountains. Some attenuation occurs when microwave energy passes through trees and frame houses. In addition, exposure to microwaves (a form of radiation) poses a health hazard and can cause nerve, fetal and DNA damage, cataracts, behavioral disturbances, changes to blood chemistry and impaired immune defense.
For example, U.S. Pat. No. 4,933,682 discloses a point to point microwave communication service antenna pattern with anull in an interfering direction that includes a microwave antenna system at each point directed at the other point, the radiation pattern of the antenna system at at least one point has a substantial null in the direction of an antenna of another microwave communication service to avoid an exchange of signals with the other service, the antenna system provided at said one point includes two antenna elements having substantially equal directional radiation patterns, so oriented and spaced apart a distance that is at least several wave length of the operating frequency of the elements so that the radiation patterns of the elements overlap producing a net radiation pattern that results from interference of the patterns and the net pattern has a substantial lobe in the direction of the other point of said service and a substantial null in the direction of an antenna of the other microwave communication service.
Another form of wireless communications is spread spectrum. Spread spectrum uses de-restricted radio frequencies and comes in two forms: direct sequencing and frequency hopping. Direct sequencing involves the use of a constant frequency for direct transmission. However, this form of spread spectrum is subject to problems such as catastrophic interference since it uses a signal whose frequency is constant. Catastrophic interference occurs when another signal is transmitted on, or very near, the frequency of the desired signal. In addition, a constant-frequency signal is easy to intercept, and is therefore not suited to applications in which information must be kept confidential between the transmitting and receiving parties.
Frequency hopping transmissions seek open frequencies and hop from frequency to frequency at split second intervals according to a specific and complicated mathematical function. Although this form of spread spectrum is more secure than direct sequencing, transmissions are secure only if the mathematical function is kept out of the hands of unauthorized people or entities. In addition, radio frequency emission is a type of electromagnetic energy or radiation, and thus is a possible health risk and cause for concern due to radiation exposure.
U.S. Pat. No. 5,854,985 discloses, an adaptive omni-modal radio apparatus and method for describing a frequency and protocol agile wireless communication product, and chipset for forming the same, including a frequency agile transceiver, a digital interface circuit for interconnecting the radio transceiver with external devices, protocol agile operating circuit for operating the radio transceiver in accordance with one of the transmission protocols as determined by a protocol signal and an adaptive control circuit for accessing a selected wireless communication network and for generating the frequency control signal and the protocol control signal in response to a user defined criteria.
U.S. Pat. No. 5,761,621 discloses a network and method of operating a network of wireless service providers adapted to interact with a plurality of omni-modal wireless products within a given geographic area in a manner to permit the wireless service providers to “borrow” radio frequencies from other wireless service providers within the same geographic region.
Another form of wireless communication is the infrared laser communication system, which is used in thousands of installations world-wide for cable-free transmission of data, voice and video at speeds from T-1 through 622 Mbps. These systems can provide a transparent and cost effective connection between buildings at distances up to 6000 meters (3.69). These free-space, optical laser communications systems are wireless connections through the atmosphere communicating via electromagnetic radiation. Infrared laser systems work basically the same as fiber optic cable except the beam is transmitted through open space rather than glass fiber. The systems operate by taking a standard data or telecommunications signal, converting it into a digital format and transmitting it through free space. Two parallel beams are used, one for transmission and one for reception. The carrier used for the transmission of this signal is infrared and is generated by either a high power LED or a laser diode. The disadvantage of this form of wireless communication, however, is the possible health risk due to emission of radiation, especially in enclosed spaces where there are numerous devices communicating with each other via infrared, which have frequencies higher than those of microwaves.
U.S. Pat. No. 5,247,380 discloses an infrared data communications network in which groups of personal computers and associated peripherals may communicate by infrared signals with each other. The system utilizes a error correction and a packet switched protocol which allows any terminal to select communications with any other terminal or terminals without degradation of the error rate. Error free transmission is maintained by means of error correcting encoding and a handshake protocol. The packet switched protocol permits any terminal to function as a store and forward repeater thus making the system less susceptible to beam blockage.
As embedded devices become more commonplace, homes and offices are becoming occupied by greater numbers of various intelligent appliances which need to communicate with each other. Using current wireless communication techniques may be a health hazard because of the high output of emitting rays in relatively small enclosed spaces. In larger amounts, microwave and spread spectrum radio waves in enclosed spaces can interfere with each other. Accordingly, an efficient, accurate and non-emitting wireless communication technique which allows embedded devices to communicate with each other is highly desirable.